The present invention relates to a burst receiving circuit and a control method of the burst receiving circuit applying for data communication apparatuses using the time division multiplex communication and so forth.
At the conventional burst light receiving circuit of the ATC (automatic threshold control) type, at the time when signals do not exist between bursts, the output becomes unstable, that means, there is no factor to decide either xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d, therefore the output is changed by the fluctuation of small conditions at the inside and outside of the circuit. In order to solve this problem, the offset is applied to the ATC circuit beforehand and this method has avoided the state of the unstable output.
However, this method applying the offset to the ATC circuit has some faults that the receiving level sensitivity becomes low and the deterioration of the output duty occurs and so forth, and the high performance of the burst light receiver has been obstructed.
It is therefore an object of the present invention to provide a burst receiving circuit and a control method thereof which avoid the unstable state of the output without bringing about the decrease of the receiving level sensitivity and the deterioration of the output duty.
According to a first aspect of the present invention, for achieving the above mentioned objects, a burst receiving circuit provides a control means for giving an offset which corresponds to the size of a receiving signal to said receiving signal, a signal shaping means for taking out a burst signal by shaping said receiving signal given said offset based on a predetermined threshold value and an offset switching means which said control means makes said offset xe2x80x9c0xe2x80x9d at the time when said burst signal is received.
According to a second aspect of the present invention, a burst receiving circuit provides a detecting means for detecting the start of said burst signal at said receiving signal.
According to a third aspect of the present invention, a burst receiving circuit provides a retriggerable multi vibrator which makes the xe2x80x9c0xe2x80x9d state of said offset continue until predetermined time passes after the finish of said burst signal.
According to a fourth aspect of the present invention, a burst receiving circuit provides a flip-flop at which an output is raised by the start of said burst signal and said output is fallen by the finish of said burst signal informed from the outside and a NAND circuit which makes the xe2x80x9c0xe2x80x9d state of said offset continue at the case that the both ouputs of said retriggerable multi vibrator and said flip-flop have been raised.
According to a fifth aspect of the present invention, a burst receiving circuit provides a light receiving element receiving a light signal and amplifiers which convert an electric current flowing in said light receiving element to said receiving signal.
According to a sixth aspect of the present invention, there is provided a control method of a burst receiving circuit, which gives an offset corresponding to the size of a receiving signal to said receiving signal and makes said offset xe2x80x9c0xe2x80x9d at the time when said burst signal is received, and takes out a burst signal by shaping said receiving signal given said offset based on a predetermined threshold value.
According to a seventh aspect of the present invention, there is provided a control method of a burst receiving circuit, which makes the xe2x80x9c0xe2x80x9d state of said offset continue until predetermined time passes after the finish of said burst signal.
According to an eighth aspect of the present invention, there is provided a control method of a burst receiving circuit, which makes the state xe2x80x9c0xe2x80x9d of said offset continue from the start of said burst signal until predetermined time passes after the finish of said burst signal, or until the finish of said burst signal informed from the outside.
At the present invention, to the receiving signal, an offset is given corresponding to the size of the receiving signal and at the time the burst signal is received, the offset becomes xe2x80x9c0xe2x80x9d And the burst signal is taken out by shaping the receiving signal given offset based on a predetermined threshold value. The offset is continued to be xe2x80x9c0xe2x80x9d until predetermined time passes after the finish of the burst signal. And from the start of the burst signal until predetermined time passes after the finish of the burst signal or until the finish of the burst signal informed from the outside, the offset is continued to be xe2x80x9c0xe2x80x9d.